3.6 Factors Influencing Enzyme Activity (2)

What is enzyme concentration?

The amount of enzyme present in a given volume of solution.
→ Determines how many active sites are available.

What is the effect of increasing enzyme concentration on rate of reaction?

The rate increases as enzyme concentration increases.
→ More enzyme molecules = more active sites = more collisions.

Why does increasing enzyme concentration increase reaction rate?

Because there are more active sites available for substrates to bind.
→ Leads to more enzyme-substrate complexes per unit time.

What condition must be met for enzyme concentration to affect rate?

The substrate must be in excess (not limiting).
→ Otherwise, increasing enzyme has no further effect.

What happens if substrate becomes limiting at high enzyme concentration?

The rate will stop increasing and level off.
→ Not enough substrate to occupy all active sites.

What does it mean that rate is directly proportional to enzyme concentration?

Doubling enzyme concentration → doubles the rate (if substrate is excess).

What is pH?

A measure of the hydrogen ion (H⁺) concentration in a solution.
→ Lower pH = higher H⁺ concentration.

What is the effect of pH on enzyme activity?

Each enzyme has an optimum pH at which it works best.
→ Activity decreases above and below this pH.

What is optimum pH?

The pH at which an enzyme has maximum activity.
→ Active site has the ideal shape at this pH.

Why does pH affect enzyme activity?

Changes in pH alter hydrogen bonding and ionic interactions in the enzyme.
→ This changes the shape of the active site.

What happens to enzymes at extreme pH values?

They become denatured.
→ Active site loses shape → substrate cannot bind.

What is denaturation?

A permanent change in the structure of an enzyme, causing loss of function.
→ Active site is no longer complementary to substrate.

Give examples of enzymes and their optimum pH.

• Pepsin → ~pH 2 (acidic, stomach)

• Catalase → ~pH 7 (neutral, cytoplasm)

• Alkaline phosphatase → ~pH 9–10 (alkaline)

What is a buffer solution?

A solution that resists changes in pH when acids or bases are added.
→ Keeps pH constant during enzyme experiments.

Why are buffer solutions used in enzyme experiments?

To ensure pH remains constant, so results are valid.
→ Prevents pH from affecting enzyme activity.

What are control variables?

Variables that are kept constant during an experiment.
→ Ensures only the independent variable affects results.

Give examples of control variables in enzyme experiments.

• Temperature

• pH

• Substrate concentration

• Enzyme concentration

Why must control variables be kept constant?

To ensure valid and reliable results.
→ So changes are due to the factor being tested only.